**3.1 Limestone as the host rock**

The host rock of Ningwu ice cave and Zibaishan ice cave mainly consists of limestone. Limestone is composed of calcium carbonate which is an unsteady material and could be readily dissolved. Limestone areas could become karst landform under wet and warm climate in the geological period. The limestone cave developed predominantly in the perpendicular direction, for example, Ningwu ice cave and Zibaishan ice cave. Generally, the karst region is not suitable for ice preservation. Ice preservation in karst cave may indicate the climate change from warm to cold globally or the presence of incomprehensible cooling mechanisms locally.
